1. Field of the Invention
This invention relates in general to radio frequency (RF) communication systems, and in particular, to a method and apparatus for fraud control in cellular mobile radiotelephone (CMR) and personal communications services (PCS) systems.
2. Description of Related Art
Cellular phones combine the mobility of the radio link and the world-wide land telephone network to provide a communication link to any other telephone in the world. However, as cellular phones have become more prevalent throughout the country, fraud has become a major problem. Cellular phone fraud robs service providers of hundreds of millions of dollars every year. Like all crimes, there are several varieties of cellular fraud, including "cloning."
Cloning fraud, which occurs when a legitimate subscriber's mobile identification number (MIN) and electronic serial number (ESN) combination is used for illegal purposes, is among the most sophisticated and difficult forms of fraud to prevent. Often, the fraudulent user will use simple electronic receivers to "capture" the legitimate MIN/ESN combination during its transmission. In these cases, the legitimate subscriber often does not know fraud is being committed. This is currently the most popular method of gaining illegal access to a cellular system because the legitimacy of the stolen MIN/ESN combinations makes cloning difficult to catch.
Techniques exist for identifying situations in which two cellular phones with the same MIN/ESN combination are making a call at the same time. Motorola Technical Education and Documentation, 68P09222A54-O, of Aug. 14, 1994 entitled "Clone Clear Feature", which is incorporated by reference herein, discloses a method of detecting duplicate MIN/ESN combinations present on a switch simultaneously and for dealing with such duplicate calls.
Duplicate calls may arise in any number of different ways. For example, a first call from a cellular phone may be disconnected because of carrier loss, wherein the cellular phone immediately attempts a second call to re-establish its connection before the switch has completely torn down the first call. In another example, interference on the channel at the base station controller causes the controller to mark the first call as active, when in fact the cellular phone has completed its first call and has started a second call. In yet another example, a fraudulent cellular phone may be illegally using the valid MIN/ESN combination.
When simultaneous, duplicate MIN/ESN combinations are detected on a switch, the first cellular phone detected, the second cellular phone detected, or neither of the cellular phones can be terminated using the Clone Clear Feature of the switch Generally, these options are left to the discretion of the switch operator.
Calls terminated by the Clone Clear Feature are typically marked with a Call Final Class (CFC) "8E" hexadecimal value in their associated call records. When this particular CFC value is present in a call record, it is usually interpreted as an unbillable call by accounting systems. Unfortunately, this results in lost revenue in the first two examples described above, where the duplicate calls arose through the actions of a legitimate subscriber without the presence of clone activity.
Additionally, inherent to the Clone Clear Feature is a situation referred to as a "glare war." There are numerous scenarios that can cause a glare war. For example, a call placed by a legitimate cellular phone may be interrupted by the activity of a fraudulent cellular phone. The legitimate cellular phone may be forcibly disconnected by the Clone Clear Feature when the call from the fraudulent cellular phone occurs on the switch. The legitimate subscriber may perceive that a dropped call has occurred (which itself is detrimental to the carrier's reputation). If the legitimate subscriber attempts to re-connect, while the call from the fraudulent cellular phone is still connected, then the Clone Clear Feature will forcibly disconnect the call from the fraudulent cellular phone. If the fraudulent cellular phone attempts to immediately re-connect, using the same MIN/ESN combination as the legitimate subscriber, it is likely the call placed by the legitimate subscriber will once again be interrupted by the Clone Clear Feature.
While the Clone Clear Feature is efficient for minimizing fraudulent use, it can cause the indiscriminate termination of calls, including those placed by legitimate cellular phones. Thus, the Clone Clear Feature has its drawbacks when used by carriers. It can be seen, then, that there is a need for fraud control techniques which terminate only fraudulent calls when duplicate MIN/ESN combinations are detected on a switch.